International astronomers, including a leading planet hunter at UC Santa Cruz, say they have detected five possible planets circling a distant star much like Earth's sun - and that one of those planets is apparently in the famed "habitable zone" where water could exist on its surface.

Visible in the evening sky and only 12 light-years from Earth, the star is called Tau Ceti. The astronomers reported Tuesday that they had combined more than 6,000 observations from three telescopes to detect the system of "exoplanets."

The astronomers estimate that the five planets range from two to six times the mass of Earth, making it a planetary system with the lowest mass of any yet detected. The planet inside the habitable zone - where, if water exists, life could also be possible - is only five times the mass of Earth, they calculate.

The telescopes used to observe the planets are located in Hawaii, Chile and Australia. The astronomers used a new technique to model their signals intensively to increase their sensitivity as they searched for planets with low masses.

"This discovery is in keeping with our emerging view that virtually every star has planets, and that the galaxy must have many potentially habitable planets," said Steven Vogt, the UC Santa Cruz astronomer on the international team.

R. Paul Butler of the Carnegie Institution in Washington, Vogt's planet-hunting colleague, is also on the team reporting the new planetary system. He said the new technique will enable the astronomers to resolve "the secrets of our nearest companion stars and their previously hidden reservoirs of potentially habitable planets."

"Just make a triangle with Jupiter on the left and the moon on the right," Frank said. "Tau Ceti is at the apex pointing down and about 5 1/2 fists extended at arms length above the horizon. It is slightly yellow in color."